1. Field of the Invention
The present invention relates to a bearing cap and, more particularly, to a cast bearing cap having precisely interfitting and mating parts and to a method for making such a bearing cap.
2. Description of the Related Art
The term "bearing cap" as used herein denotes a device used to surround, support, and guide a rotating or reciprocating shaft. A typical use is at a point of penetration of the shaft through a housing or enclosure such as at the passage of a camshaft or crankshaft through an engine block. Another typical use is at the passage of a crankshaft through a piston connecting rod. The bearing cap may make direct contact with the shaft, or, as is more frequently the case, the bearing cap may surround a bearing which, in turn, directly contacts the shaft. In either event, the bearing caps must be manufactured to close tolerances in order to provide a close, uniform fit around the shaft or bearing.
Bearing caps are frequently formed as split rings having two parts surrounding the shaft or bearing and joined together along a diametric line. With such split rings, not only must the central bore fit closely to the shaft or bearing, but the parts of the caps must fit precisely together at the mating surfaces of the parts of the caps. If the parts of the caps are manufactured separately and individually for subsequent machining and assembly, it is difficult to maintain the tolerances necessary to provide a sufficiently precise fit.
It has been proposed in the prior art to manufacture a two part bearing cap from a unitary bar stock or a cast unitary metal ring. The two parts of the bearing cap are made by first defining a diametric fracture plane by forming weakened diametric notches or grooves on the outer surfaces of the ring on either side of the central opening of the ring. Force is applied to the portions of the ring at opposite sides of the notches or grooves sufficient to fracture the ring along the fracture plane and form two separate ring halves. The intended result of this method is that the fractured diametric surfaces of the ring halves will mate precisely when the ring halves are placed around a shaft or bearing and brought back together.
In practice, however, the aforementioned prior art method has significant drawbacks. First, when the ring is fractured, the metal at the fracture surface is frequently splintered or distorted. Because of this distortion, the fracture surfaces do not precisely mate together when the ring halves are brought together. Second, since the ring must be fractured across its entire diametric cross-sectional area, the force required to produce the fracture is huge. Such force is concentrated at the points where the fracturing device contacts the ring, thus causing the ring to bend and lose its desired dimensions. Third, an embedded steel reinforcing insert may not be used since the internal boundaries between the steel insert and the surrounding cast metal will define stress lines. The ring will tend to fracture along these stress lines rather than along the intended diametric plane.
In another prior art method of manufacturing a two part bearing cap, two semicylindrical halves are first formed separately. The mating diametric surfaces of each half are machined and bores are drilled into the surfaces. Dowels are inserted into the bores and the two halves are assembled together aligned by the dowels. Next, the central opening of the assembled bearing cap is machined to the desired diameter and finish. The halves are then disassembled.
This second prior method also presents significant drawbacks. The method is quite costly, requiring dowels, a step of machining the four mating surfaces, and a step of drilling the four bores for the dowels. Several close tolerances must be held, including the positioning and diameter of the dowel bores and the flatness and orientation of the mating surfaces. A step of assembling bearing cap parts is required before the central opening can be machined, and it may be necessary to bolt the bearing cap parts together before the machining can be done.
Accordingly, there is a heretofore unmet need for a bearing cap having parts which precisely intermit and an economical method for making such a bearing cap.